Hybrid powertrains use multiple sources of input torque as needed in order to optimize fuel economy. Typically, an internal combustion engine provides input torque at higher vehicle speeds, either alone or assisted by additional input torque from an electric traction motor. The engine may be turned off at idle to conserve fuel. The traction motor may be used at low speeds to propel the vehicle in an electric-only mode, with the engine automatically restarting above a threshold speed or a threshold output torque request. In mild hybrid configurations, the traction motor is not used to propel the vehicle, but is still used to crank and start the engine after an engine autostop event. Extended-range electric vehicles provide yet another powertrain design in which a small internal combustion engine is used to generate electricity for powering the traction motor and/or for recharging a high-voltage battery.
In all of the example hybrid powertrain types noted above, a hybrid thermal system is used to cool various devices. Such fluid-cooled devices may include, for example, power inverter modules, auxiliary power modules, energy storage systems, the traction motor(s), and the like. A typical hybrid thermal system uses multiple cooling actuators. For instance, a fluid pump and one or more fans or blowers may circulate cooling fluid through different thermal loops. Proper thermal management of the various fluid-cooled devices is essential to ensuring the optimal performance of the hybrid powertrain.